Multivibrator trigger circuit



B. l., HAVENS vII/IUI.'1IV1I3R.LIT0R TRIGGER CIRCUIT Filed Dec. 21, 1951May 15, 1956 United States Patent O MULTIVIBRATOR T RIGGER CIRCUIT ByronL. Havens, Closter, N. J., assignor to International Business MachinesCorporation, New York, N. Y., a corporation of New York ApplicationDecember 21, 1951, Serial No. 262,733v

7 Claims. (Cl. 250-27) This invention relates to electronic switches andmore particularly to an improved electronic switch having two stableconditions and employing a trigger circuit or a mulitvibrator.

It is well known in the art that the speed of operation ot' a triggercircuit of the Eccles-Jordan type is less than that of a similarmultivibrator. For numerous switching purposes the multivibrator cannotbe used because it is free running and does not therefore alternatelyassume two stable conditions.

Accordingly, the principal object of this invention is to provide anelectronic switch having the operable speed of a multivibrator and twostable conditions alternately assumed by selective pulsing.

Another object is to provide a trigger circuit operable in response topulses from a single source wherein means are provided between thesource and its common conection to a plurality of points within thetrigger circuit to automatically apply each pulse to a selected one ofsaid points determined by the stable condition of the trigger circuit.

Another object is to provide a trigger circuit employing two gridcontrolled tubes and having two stable conditions alternately assumedwherein the voltage excursion at the control grid of each of the tubesis limited during operation of the trigger circuit, thereby decreasingthe recovery time of the trigger circuit.

Another object is to provide a novel trigger circuit employing two tubesand having two stable conditions alternately assumed in which the actualtriggering element per se is a multivibrator.

A further object is to provide a novel trigger circuit including amultivibrator having two stable conditions and a faster speed ofoperation than the corresponding trigger circuits or" the prior art.

A still further object is to provide a trigger circuit employing aconventional multivibrator wherein the control grids of the tubes of themultivibrator are connected through resistors to a source oi voltagesupply to maintain the conductive tube of the multivibrator in itsconductive condition until a subsequent pulse is applied to themultivibrator, and to provide clamping tubes to clamp the non-conductivetube of the multivibrator in its nonconductive condition until asubsequent pulse is applied, each of said clamping tubes being eectiveto override the-action on the non-conductive tube of each of saidresistors.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of example, the principle of the invention andthe best mode, which has-been contemplated, of applying that principle.Other embodiments of the invention employing the same or equivalentprinciple may be used and structural changes made as desired by thoseskilled in the art without departing from the present invention andwithin the spirit of the appended claims.

In the drawings:

Fig. l is a circuit diagram of a trigger circuit showing one embodimentof the invention, and

Fig. 2 is a circuit diagram showing another embodiment of the invention.

Briefly, this invention includes circuit means for limiting the negativevoltage excursion on the grid of the nonconductive tube of a triggercircuit thereby permitting the voltage at that grid to be raised aboveits cutoff value when the trigger circuit is pulsed in less time andwith greater ease than would otherwise be the case. Such limitation ofthe voltage excursion therefore decreases the recovery time of thetrigger circuit thereby providing for faster speed of operation inresponse to an input pulse of lesser amplitude. The common input to thetrigger circuit of the invention is applied thereto at a plurality ofchosen points. Means are provided between these points and the commonoutput to actually apply the input pulses to the single point which isthen at such a polarity that the application of the input pulse theretowill effect a switching of the trigger circuit from one stable conditionto the other.

These desirable features are also employed in a multivibrator circuitwhich the invention employs as a trigger circuit having two stableconditions alternately assumed. The control grids of the tubes of themultivibrator circuit are each connected through a resistor to a sourceof positive voltage to insure that the grid of the conductive tube ofthe multivibrator continues to have a positive voltage applied thereto.Clamping tubes are employed in a novel manner to override or counteractthe effect of the resistor connected to the non-conductive tube therebypreventing any substantial change in the voltage at the control grid ofeither tube of the multivibrator until an input pulse is applied to themultivibrator.

Referring to Fig. l the trigger and keying circuit comprise the twotriode trigger tubes shown in the single envelope T10, the left andright tube sections being designated by 10L or IGR respectively, and thekeying tube by KT.

The grid of each of the tubes lilL and lill?. has a parasitic suppressorresistor 1l connected thereto. The grid of the tube 10L is alsoconnected through a resistor 12 and a capacitor 13 in parallel therewithto the plate of the tube 10k and the grid of the tube MBR is connectedthrough a like resistor 14 and a like capacitor l5 in parallel therewithto the plate of the tube itil.. The grid of the tube IGR is alsoconnected through resistor 16 to a source of suitable negative voltage,say 330 volts, the grid of the tube 10L is connected through a likeresistor 17 to the same voltage source. These control grids are alsoconnected through the rectitiers 19 and 20 and their point of commonjuncture is connected through a resistor 21 to a suitable source ofnegative voltage, say 2O volts. The plate of the tube NBR is connectedthrough resistors 22 and 23 to a suitable source of plate supplyvoltage, say volts and the plate of the tube 3.0L is similarly connectedthrough resistors 24 and 23. The juncture of resistors 22 and 24 isconnected through capacitor 25 to ground to provide decoupling fromcircuits external to the trigger circuit.

The plates of the tubes 10i. and lllR are also connected togetherthrough the rectifiers 27 and 28 respectively and the juncture connecteddirectly to the plate of the keying tube KT. The plate of the tube KT isalso connected through load resistor 29 to the source of positive platesupply voltage to which the grid #2 of tube KT is also connected. Thecathode of tube KT is connected directly to ground as is the commoncathode of tube T10. The grid bias resistor 3l is connected to groundand through grid bias resistor 32 to a source of negative voltage, say-150 volts. The grid #l of tube KT is connected directly to the junctureof resistors 31 and 32.

a The grid #3 (suppressor grid) of the tube KT is connected to aterminal sg and grid #l (control grid) is connected to a terminal cgthrough condenser 32a. Theterminals sg and cg are provided to receivepositive voltages so that the keying tube l T may be rendered conductiveat preselected times when such positive voltages are simultaneouslyapplied to the two terminals. The terminals Lg and Rg connected to thecontrol grids of tubes lilL and MR respectively are provided to conveyoutputs from those respective tubes.

ln operation the trigger circuit associated with the tube T performs ina manner very similar to that of a conventional Eccles-Jordan triggercircuit in that the trigger circuit alternately assumes each of twostable conditions in response to the plate current conduction of thekeying tube KT. When in one of these stable conditions the tube 1.0L isconductive and the tube 1G12 is non-conductive. This condition isreferred to herein as the Left condition. When in the other stablecondition the tube 10i. is non-conductive and the tube TOR isconductive. This condition is referred to herein as the Right condition.The trigger circuit may be initially placed in one chosen stablecondition by any conventional means, such as, temporarily applying adifferent grid bias to the two tubes 10K and 101,. Assuming that thetrigger circuit is in the Left condition, the voltage at the plate ofthe conductive tube 1.0L is low, the voltage of the non-conductive tubei011 is high, the voltage at the terminal Lg is high, and the voltage atthe terminal Rg is low.

When suitable positive pulses are simultaneously applied to theterminals cg and sg of the keying tube KT that tube is rendered platecurrent conductive and accordingly produces a voltage drop at thejuncture of rectifiers 27 and 2S. Obviously, since the trigger circuitis in the Left condition the inverse voltage drop across the rectier 28prior to conduction of the tube KT is less than that across therectifier 27. Hence, conduction results through the rectifier 28 tolower the voltage at the grid of the tube 10L. As a result conductionthrough tube 1.0L is decreased and the corresponding voltage increase atits plate is transferred through resistor 14 and capacitor 15 inparallel therewith to the control grid of the tube 10K to render itconductive. The corresponding voltage decrease at the plate of tube 10Ris transferred through resistor 12 and capacitor 15 in parallel to thecontrol grid of the tube 161. to render it still less conductive. Thiscumulative action is continued until the tube iL is renderednon-conductive and the tube 10R is rendered fully conductive to placethe trigger circuit in the Right condition.

Since, the rectifier 27 is connected between the platey of the tubelltiL and the plate of the tube KT and since both these plates are atrelatively low voltages when the trigger circuit is keyed from the Leftcondition the keying voltage applied to the grid of the tube llL is notapplied to the tube ltlR. Hence, the voltage drop at the juncture ofrectiers 27 and 28 is routed to the grid of the conductive trigger tubeand is not applied to the grid of the non-conductive trigger tube. Therectiers 27 and also prevent the voltage at the plate of the keying tubeKT from decreasing below the voltage at the plate of the correspondingtubes 10L and 10K respectively. Such is the case because when thevoltage at the plate of the tube KT tends to become less than that atthe plate of either of the tubes itil. or 10K current is passedtherethrough tending to equalize the voltage difference between therespective plates. This selective application of pulses from a commonsource to the grids of the tubes 10T. and 10R permits a more positiveswitching of the trigger circuit than is realized when each pulse fromthe common source is applied to both tubes.

The rectiers 19 and 20 are provided to limit the voltage excursion atthe control grid to which each is connected to -20 volts which is thevalue of the voltage commonly applied to the other terminal of therectiers.

This limiting of the voltage excursion decreases the recovery time ofthe trigger circuit and therefore permits a faster switching thereof.

It is now clear that each simultaneous application of suitable positivepulses to the terminals sg and cg connected to the keying tube KT causesan output pulse to appear at each of the terminals Lg and Rg. When thetrigger circuit is switched to the Right condition the output pulse atthe terminal Lg is negative and that at the terminal Rg is positive andwhen the trigger circuit is switched to the Left condition the polarityof these respective output pulses is reversed.

Referring to Fig. 2 the trigger circuit includes a keying tube KT whichfunctions as the keying tube KT shown in Fig. l. The tubes 10T. and lRare connected to function as a multivibrator. The multivibrator crcuitis similar to the trigger circuit of Fig. l except that the resistiveconnection between the plate of each tube and the control grid of theother is omitted. This is a conventional change to effect conversion ofa trigger circuit to a multivibrator circuit.

The trigger circuit of Fig. 2 retains the desirable features of amultivibrator in that there is no resistive coupling between the plateof each trigger tube and the control grid of the other. The frequentlyobjectionable feature of a multivibrator used as an electronic switch.namely, that it is free running and cannot be switched from one stablecondition to the other, is overcome by the use of clamping tubes 35 and36.

The plate of each of the tubes 35 and 36 is connectedV through therespective rectitiers 20 and 19 and the resistor 21 to a suitable sourceof negative supply voltage, say -20 volts. The cathode of the tube 35 isconnected to a suitable source of negative voltage, say volts, throughthe resistors 41 and 42 and the cathode of tube 36 is similarlyconnected through the resistors 43 and 44. The control grid of tube 35is connected through a resistor 46 to the junction of resistors 43 and44 and the control grid of tube 36 is connected through a resistor 45 tothe juncture of resistors 41 and 42.

The cathode of tube 35 is also connected through a resistor 48 to thecathode of cathode follower tube CF50 and the cathode of tube 36 isconnected through a resistor 51 to the cathode of cathode follower tubeCF52. The plates of the tubes CPS() and CFSZ are connected directly tothe +150 volt supply. The grid of the tube 10K, the plate of the tube36, and the grid of the tube CF52 are commonly connected through aresistor 54 to a suitable source of positive supply voltage, forexample, +150 volts. The grid of the tube 10L, the plate of tube 35, andthe grid of tube CF50 are commonly connected through a resistor 55 tothe +150 volt supply. The cathodes of the tubes CF50 and CFSZV areconnected to output terminals CFL and CFR respectively.

The cathode follower tubes CFSG and CF52 are both always conductiveregardless of the conductive condition of tubes 10L, 10R, 35 and 36. Theconductivity of tubes CF50 and CF52 is indicated by an X to the lowerleft of the respective tubes. When the multivibrator tube 10L isconductive the tube 35 is non-conductive and when the multivibrator tube10R is conductive the tube 36 is non-conductive. The rcctiers Z0 and 19are connected between the -20 volt supply and the control grids of thetubes 10L and 10K tend to prevent those control grids from going belowthe -20 volts and therefore determine the most negative positions of thegrids of the multivibrator tubes IGL and 10K. The rectiiiers preventthose grids from reaching a voltage as negative as they would otherwisereach, it therefore takes less time and less power for a pulse to eect aswitching of the multivibrator from one stable condition to the otherthan would be the case if the rectiers were not employed.

In operation, the cathode follower tubes CFS() and CFSZ are alwaysconductive. For purposes of explanation, it is assumed that the tubes10L and 36 are initially conductive, as indicated by the x to the lower.left of the respective tubes, and the tubes K and 35 are initiallynon-conductive. When the l-:eying tube KT is rendered plate currentconductive, as previously described, a decreased voltage is applied tothe commonly connected terminals of the rectiers 27 and 28 and tends tocause conduction through a preselected one of the rectiers as set forthpreviously herein. A negative pulse is transferred through the capacitor13 to the control grid of the tube 1M.. Conduction through the tube 10Lis decreased and a positive voltage is transferred through capacitor 15,connected to its plate, to the control grid of the tube 10k to render itconductive.

The accumulative action above described then switches the multivibratorto the Right condition. This condition causes a positive voltage to beapplied to the control grid of the cathode follower tube 0F52 to renderit more conductive and a negative voltage to be applied to the controlgrid of the cathode follower tube CFSU to render it less conductive. Theresulting increased voltage at the cathode of tube CFSZ is transferredto the terminal CFR and through voltage dividers to the cathode ofclamping tube 35 and the control grid of clamping ltube 35. Thedecreased voltage at the cathode of the tube CFSi is transferred to theterminal CFL and through voltage dividers to the grid of clamping tube36 and the cathode of clamping tube 35.

The effect of this simultaneous application of these voltages to thetubes 35 and 36 is twofold. The applicacation of these voltages to thegrid and the cathode of the tube 36 sudiciently increases or raises thepotential of the cathode relative to the grid to thereby render the tube36 non-conductive. The application of these voltages to the control gridand cathode of the tube 35 renders tube 35 conductive. the tube 35 isapplied to the control grid of the cathode fololwer tube CFSB and thecontrol grid of the multivibrator tube ML. This current counteracts thetendency of the current through resistor 55 to hold these gridsat avoltage as near +150 volts as the grid current of multivibrator tube3.0L will permit. The steady plate current drawn from the control gridcircuit of the tube 10L by tube 35 when it is conductive assures thatthe grid of the vtube GL will remain below cut ofrr and that themultivibrator will remain in the Right condition until the keying tubeKT is again rendered conductive. The non conduction of tube 36 permitsthe current through resistor 54 to tend to raise the voltage at thecontrol grid of the tube MR thereby insuring that the voltage on thatcontrol grid will remain suiciently positive to cause conduction throughthe tube lR until keying tube KT is again rendered conductive.

Subsequent plate current conduction of the keying tube KT will in likemanner cause a switching of the stable condition of the multivibratorfrom the Right condition to the Left condition, render clamping tube 35non-conductive and clamping tube 36 conductive, decrease the conductionthrough cathode follower tube C1352, increase the conduction throughcathode follower tube CFS() and provide increased and decreased voltagesrespectively at the terminals CFL and CFR. It is now clear that theclamping tubes 35 and 36 function to relieve the positive voltagelocking action of the resistor 54 or 5S on the control grid of thenon-conductive multivibrator tube and permit a locking of positivevoltage at the control grid of the conductive multivibrator tube andeffect a locking of negative voltage at the control grid of thenonconductive multivibrator tube between periods of conduction of keyingtube KT.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in theart, without The resulting plate current of r departing from the spiritof the invention. It is the intention, therefore, to be limited only asindicated by the scope of the following claims. i

What is claimed is:

1. An electronic switching circuit having two stable conditionsrepresented by an alternate conduction and non-conduction of each of twogrid controlled tubes; a source of pulses for switching said circuitfrom each stable condition to the other; means consisting only of a pairof rectifers and a resistor connected between the control grid of eachof said tubes and a first constant potential for limiting the .negativevoltage excursion thereon to a predetermined value thereby decreasingthe recovery time of said circuit; means directly connecting thecathodes of each of said tubes in common to a second constant potentialsuch that said cathodes are at all times maintained at said secondconstant potential; and a rectifier connected to the control grid ofeach of said tubes and said source so that each pulse from said sourcewill .be applied only to the control grid having the most positivevoltage thereon. v

2. In a trigger circuit having two grid controlled tubes and two stableconditions alternately assumed in response to each selected pulseapplied thereto; rectiers connected between the control grid of each ofsaid tubes andv a source of constant bias voltage to limit the voltageexcursion on said grids to a value at least as positive as the voltagevalue at said source; circuit means for maintaining the potential of thecathodes of each of said tubes at a constarrt value; a coupling networkconnected between the plate of each tube and the control grid of theother; a source of pulses for switching the trigger circuit fromV onestable condition to the other and connections therefrom to an inputterminal; and pulse selective mean-s responsive to apredeterminedvoltage difference thereacross and connected between said terminal andeach of said tubes so that a single selected pulse is applied to apreselected one of said tubes to switch said trigger circuit from eachstable condition to the other, said preselected tube being determined bythe stable condition of said trigger circuit.

3. An electronic switch operable in response to preselected voltagepulses and having two stable conditions including a free runningmultivibrator having two crossconnected grid controlled tubesalternately conductive and non-conductive and vice versa; and means foralternately holding each of said tubes in a conductive andnon-conductive condition and vice versa to represent said two stableconditions, said means including two electronic clamping tubes eachhaving an electrode coupled to a different one of the grid controlledtubes of the multivibrator so that a certain predetermined voltagechange at either of said grid controlled tubes is transferred to saidclamping tubes to reverse the conductive condition of each of theclamping tubes, and a connection from each clamping tube to a ditferentone of said grid controlled tubes to transfer a steady voltage theretothereby preventing said grid controlled tubes from automaticallychanging their conductive condition.

4. The electronic switch set forth in claim 3 wherein each clamping tubeis coupled to the control grid of a dilerent one of the grid controlledtubes through a cathode follower tube having its control grid connecteddirectly to the control grid of one of the multivibrator tubes and alsoconnected to a source of positive voltage through a resistor; and thecathode of each cathode follower is connected to the cathode of oneclamping tube and a grid the vcontrol grid of a cathode follower tube tochange the conductivity of the latter when the conduction of the tube ofthe multivibrator connected thereto is increased in response to aV pulsefrom said source; two grid controlled tubes, each having its controlgrid and cathode connected to the cathode of a different one of saidcathode follower tubes so that a change in the conductivity of one ofsaid cathode follower tubes effects opposite conductive changes in eachof said clamping tubes thereby changing the conductive condition of eachof the clamping tubes; and a connection from each clamping tube to adifferent one of the tubes of the multivibrator to transfer a voltagechange to the latter to counteract the effect of the voltage appliedthereto through said resistive connection and apply vol*- age ofsuitable polarity to the tubes of said multivibrator to effect aswitching thereof to the other conductive condition in response to eachof said pulses and apply voltages of suitable polarity to effect aholding of each of said tubes in that condition of conductivity untilthe next subsequent pulse is applied to said multivibrator.

6. In a trigger circuit employing a multivibrator having a firstgrid-controlled tube and a second grid-controlled tube; a source ofinput pulses, electronic circuit means for causing the multivibrator toalternately assume each of two stable conditions in response to inputpulses applied thereto; a clamp circuit means including a first triodehaving an anode, a cathode and a control grid, a second triode having ananode, a cathode and a control grid, a rst resistor connecting thecathode of said first triode tothe control grid-of said second triode, asecond resistor connecting the cathode of said second triode to thecontrol grid of said first triode, a direct connection between the anodeof said first triode and the control grid of said iirst tube and adirect connection between the anode of said second triode and thecontrol grid of said second tube, whereby each of said-pulses is appliedto a preselected point of the multivibrator as determined by the stablecondition thereof.

7. An electronic switching circuit including a multivibratorhavingftirst and second cross-connected grid controlled tubes; a sourceof input pulses and a connection therefrom to a plurality of points ofthe multivibrator having different voltages applied thereto; rectifiermeans connected between said source and said points to apply each ofsaid pulses to the one of said points at which is present an extremevoltage value; a holding resistor connected to a source of positivevoltage for holding each tube of said multivibrator in its conductivecondition; and pulse responv Vsive electronic means including a rsttriode having an anode, a cathode and a control grid, a second triodehaving an anode, a cathode and a control grid, a first resistorconnecting the cathode of said first triode with the control grid ofsaid-second triode, a second resistor connecting the cathode ofsaid'second triode with the control grid of said first triode, a directconnection between the anode of said rst triode and the control grid ofsaid first grid-controlled tube, and a direct connection betweentheanode of said second triode and thc control grid of said secondgridcontrolled tube, whereby the holding action of said holding resistoris relieved when each input pulse is applied to each of said points ofsaid multivibrator.

References Cited in the ile of this patent Y UNITED STATES PATENTS2,441,579 Kenyon May 18, 1948. 2,545,924 Johnstone Mar. 20, 19512,568,918 Grosdoif Sept. 25, 1951 2,580,771 Harper Ian. l, 1952 OTHERREFERENCES Proc. of the I. R. E., December 1950, vol. 38, pages1422-1427, A Ditigal Electronic Correlator, by Singleton.

